1. Field of the Invention
The present invention relates to a device and method for the detection and measurement of nitric oxide, nitrogen dioxide or nitrogen oxides (NOx) in a gaseous medium. More particularly, the invention is directed to the detection of these oxides of nitrogen in the presence of high concentrations of carbon monoxide.
2. Discussion of the Prior Art
In recent times, a greater awareness has developed regarding the dangers of air pollution, particularly in urban or industrialized areas. Amongst the principal contributions to air pollution are the products of incomplete combustion such as carbon monoxide, hydrocarbons, carbonaceous particulate matter, etc. Attempts to eliminate these pollutants through more efficient combustion processes has resulted in a frustrating dilemma for the severe oxidation conditions ordinarily employed in more efficient combustion processes increases noxious NO and NO.sub.2 gases produced over and above that ordinarily formed as combustion by-products. It is not surprising, therefore, that most major cities yearly average nitrogen dioxide levels are approaching levels known to be harmful to health.
In order to meet the needs arising in connection with pollution control of NO and NO.sub.2, extensive activity has been directed to the development and production of equipment useful in solving this problem. A problem encountered in the development of such equipment is the difficulties experienced in the detection of low concentrations of NO and NO.sub.2 in the presence of high concentration of CO, a frequently encountered situation. For instance, Oswin et al in U.S. Pat. No. 3,776,832 teaches use of a three electrode system employing a gold working electrode and a fixed potential of 1.0 V to 1.3 V for the detection of nitric oxide. While an effective sensor of nitric oxide in other gaseous media, it has its shortcomings in the detection of small amounts of nitric oxide in gaseous mixtures containing high concentrations of carbon monoxide.
Also, another problem which must be confronted in the search for solutions to this problem is the acknowledged difficulty of measuring NO in the presence of NO.sub.2. Although systems may exist which may be considered functionally successful, actual utilization in practical applications has quite often been thwarted due to the cost and complexity of such equipment.
The general criteria applied to measuring and testing equipment such as that of the present invention includes requisites for portability, non-prohibitive cost and accuracy in measuring the quantity of the gas detected. In the prior art, it has been found difficult to simultaneously fulfill all of these requirements. Increasing the accuracy of measuring equipment has inherently involved an increase in either the size or the complexity of such equipment thereby disadvantageously affecting either the cost or portability or both. Quite often, problems related to the simultaneous provision of these features have been decisive in obstructing the practical development and utilization of particular detection apparatus.